Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$12.46	9.222%	$13.6091	$13.61	$13.60	$13.60
Purchase #2	$233.46	8.495%	$253.2924	$253.29	$253.30	$253.30
Purchase #3	$209.77	6.515%	$223.4365	$223.44	$223.45	$223.40
Purchase #4	$173.33	4.617%	$181.3326	$181.33	$181.35	$181.30
Purchase #5	$58.57	5.432%	$61.7515	$61.75	$61.75	$61.80
Purchase #6	$52.57	8.321%	$56.9443	$56.94	$56.95	$56.90
Purchase #7	$215.73	11.726%	$241.0265	$241.03	$241.05	$241.00
7 purchase totals =	$955.89		$1,031.3929	$1,031.39	$1,031.45	$1,031.30